Cardiorespiratory and Hematological Responses to High-Intensity Interval Training in Adolescent Girls With Overweight or Obesity: A Randomized Controlled Trial.

This randomized controlled trial examined the effects of a 10-week high-intensity interval training (HIIT) program on physiological and hematological outcomes in 28 adolescent girls with overweight or obesity. Participants were randomly assigned to a HIIT group or a control group. The HIIT protocol comprised 4 sets of 6 × 15-s bouts at 90%-105% of maximal aerobic speed (MAS), interspersed with 15-s active recovery at 50% MAS, performed three times per week. Significant group×time interactions were observed for body composition, aerobic capacity, maximal heart rate (HRmax), erythrocytes, hemoglobin, hematocrit, creatine kinase (CK), and lactate dehydrogenase (LDH). Between-group comparisons showed greater improvements in body mass, body fat, waist circumference, MAS, estimated VO2max, and plasma volume in the HIIT group compared with controls, though not all differences reached statistical significance. Within-group analysis in the HIIT group revealed reductions in body mass (p < 0.001, d = 0.37), body fat (p = 0.001, d = 0.78), waist circumference (p < 0.001, d = 0.54), HRmax (p = 0.020, d = 0.88), erythrocytes (p = 0.007, d = 0.46), hemoglobin (p = 0.019, d = 0.84), hematocrit (p = 0.004, d = 0.34), CK (p = 0.049, d = 0.29), and LDH (p = 0.032, d = 0.41), alongside increases in MAS (p = 0.007, d = 0.64) and estimated VO2max (p = 0.007, d = 0.64). Plasma volume variation was also higher in the HIIT group. Overall, a 10-week HIIT intervention enhanced body composition, plasma volume, and cardiorespiratory fitness, while reducing markers of muscular and metabolic stress. These results indicate that HIIT is a feasible and effective approach for improving physiological and metabolic health in adolescent girls with overweight or obesity, supporting its potential as a targeted exercise strategy in this population.